1. Field of the Invention.
The present invention relates generally to packaging techniques for integrated circuits (ICs), and more specifically, to a method of using standard interconnect chips and Tape Automated Bonding (TAB) frames to implement mask-programmable interconnects for multi-chip module.
2. Description of Related Art
Packaging is considered by many in the industry to be the pacing technology for IC development. Advances in packaging have led to multi-chip modules for complex digital systems. Two of the principal problems facing developers of multi-chip modules are cost and development time.
There are a number of impediments which must be overcome before multi-chip modules will be used in volume by the commercial segment of the computer industry. One impediment is the increased development time required to design and fabricate a system based on multi-chip modules relative to the time required for an equivalent system based on PC boards. Another impediment is the high cost of substrates for multi-chip modules relative to the cost of an equivalent PC board. Still another impediment is the additional cost of TAB packaging for die mounted on the multi-chip modules.
Balancing these impediments to the use of modules, there are obvious problems with the use of PC boards in high performance systems. One problem is the longer time required to design and fabricate a PC board system having equivalent performance to a system based on multi-chip modules. Another problem is the high cost of the exotic materials required to construct a PC board system having the equivalent performance of a system based on multi-chip modules.
Taken altogether, the impediments to the use of modules are slowly being overcome through technology and infrastructure development, while the problems in utilizing PC boards are growing worse as system performance improves. In addition, there are some system level cost advantages for multi-chip modules that improve their long term economic outlook. One cost advantage is the lesser development time required to design and fabricate a PC board system having the equivalent performance of a system based on multi-chip modules. Another cost advantage is that the reduction in heat dissipation for a system based on multi-chip modules makes such a system more acceptable in an office environment where high performance systems add to the cooling load on the building's air conditioner. Still another cost advantage is the size reduction due to multi-chip modules, which reduces the cost of system level packaging. Yet another cost advantage is the inherent reliability of thermal compression interconnect bonds used in multi-chip modules, which reduces the system repair cost in the field.
While none of these considerations, in themselves, are serious impediments today to the use of systems based on PC boards, the next generation of electronics will have more functionality, larger die size, and require more heat dissipation, unless steps are taken in their design to reduce some of these factors. Although it is difficult to be precise without having actual design examples, it is not unreasonable to expect that multi-chip modules will achieve a factor of two to five increase in system speed and logical complexity without a corresponding increase in power levels.
Table I provides a summary of cost estimates for constructing a PC board system as compared to a system based on multi-chip modules. The PC board is estimated to be a 20 inch multi-layer board, while the module is 125 mm square. The PC board cost is estimated at $1.00 per square inch, while the multi-chip module cost is estimated at $3.20 per square centimeter. The increased cost of using TAB (due to its current low incidence of use) shows up in the increased cost of ICs in a system based on multi-chip modules. As can be seen from Table I, when all of these costs are taken into consideration, a system based on multi-chip modules is about equal in cost to a system using a PC board. If multi-chip modules can compete on the basis of total system cost, then the increased design cycle time becomes the principal impediment to their use in digital systems.
TABLE 1 ______________________________________ Relative Cost Component PC Board System Module System ______________________________________ Substrates $400.00 $500.00 Integrated Circuits 1000.00 1200.00 Other Components 200.00 100.00 Assembly & Test 100.00 150.00 Connectors 200.00 150.00 Backplanes 100.00 25.00 Power Supplies 100.00 50.00 System Packaging 50.00 25.00 Cost of Ownership 25.00 10.00 (reliability) Environmental Factors 25.00 10.00 TOTAL SYSTEM COST $2200.00 $2220.00 ______________________________________